When you take a dead fish and jerky off a hobo with it.

Mercury retrograde is the act of taking a shit whilst mooning one or more human beings. Your day can typically being going well, according to your horoscope, until you are forced into witnessing Mercury retrograde. Performing Mercury retrograde will often speed the astrological cycle forward for the individual performing the Mercury retrograde, bringing about happy and fruitful times to come.

The sexual act is based upon the 'Splashing around' Pokemon Magikarp.

Magikarping or to Magikarp a person, is for one to continue sex until the moment in which you are to ejactulate, at which moment you must pull and and flop your penis in the pool of sperm you have just released upon the partner, whilst shouting 'Magikarp-karp-karp' and like Magikarp noises

It can be seen as a legendary act if carried out and a humiliation to the victim

The action of lying on the ground, on your belly or your side with your hands either together above your head or on your sides, then flailing as to simulate the pokemon "magikarp" using splash attack. or any fish in general.

The start of this seems to be from anime conventions and a spin-off and response to planking, as the action is usually recorded not photographed.

When a person goes fishing, but the intent is to stick a penis in a fish

When you flop around on your partner like a Magikarp, thus entering the sex position Magikarping (WARNING: May cause you to evolve into a Gyarados and use Hydro Pump)

Magikarping is a technique in Grand Theft Auto V, it means to jump and then flopping mid-flight to achieve laughs or in some cases injure people who you go into.